Wave guide seal and filter structure



Dec. 28, 1954 J. KLlNE ETAL 2,698,421

WAVE GUIDE SEAL AND FILTER STRUCTURE Filed May 23, 1952 I 19770 IVE) United States Patent WAVE GUIDE SEAL AND FILTER STRUCTURE Jack Kline, Concord, and Albert D. La Rue, Lexington, Mass., assignors to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application May 23, 1952, Serial No. 289,689

3 Claims. (Cl. 33373) This invention relates to devices adapted to couple the output of a source of electromagnetic energy, such as a magnetron, to a load.

In such devices, it is necessary to transform the high impedance level of the load circuit to a lower impedance level required of the source, such as one of the resonant cavities of a magnetron, with a minimum of loss while preserving the vacuum in the interior of the magnetron. Heretofore in such devices it has been necessary to insert a complicated system of choke joints in the neighborhood of the seal. These choke joints introduce losses into the system but are needed to allow the coupling device to be made vacuum tight and still connect to the load. It has been found necessary to leave spaces between the coupling materials and the vacuum sealing materials in order to allow for a dilferent coefiicient of expansion of the two materials. The chokes are designed to prevent these spaces from having undesirable efiects on the electrical characteristics of the system. Another difficulty with such a construction is that it is likely to bring conductive surfaces at different potentials close enough together to allow arcing.

These difficulties are overcome in the structure of the present invention by making the output guide circular and of a material, such as the alloy known as Kovar, having approximately the same coefiicient of expansion as the ceramic used for the seal or window and by arranging the components such that the circular wave guide serves to provide both the vacuum seal and the connection to the load. This permits the ceramic to be sealed directly to the interior walls of the wave guide section without the use of chokes. The inner end of the wave guide is joined directly to the impedance transformer section, which in turn is joined directly to an opening in the back of a resonant cavity of the magnetron. This impedance transformer section performs the function of transforming the impedance levels of the load and source. By appropriate selection of the diameter of the circular wave guide, the thickness of the dielectric seal and the proper positioning of the seal with relation to the impedance-transformer section, such a device can be made to selectively 4 couple the energy at the desired frequency to the load. The result is a simple, cheaply made output structure constructed with a vacuum-tight seal and a minimum of electrical losses and danger of arcing. This structure is capable of preferentially coupling energy from a source to a load.

The foregoing and other advantages, objects, and features of the invention will be better understood from the following description taken in conjunction with the accom anying drawings, wherein:

Fig. 1 is a section taken along the line 1--1 of Fig. 2 of one embodiment of the invention;

Fig. 2 is a section taken along the line 22 of Fig. 1;

Fig. 3 is a section of a second embodiment of the invention taken along the line 3-3 of Fig. 4; and

Fig. 4 is a section taken along the line 44 of Fig. 3.

In Fig. l, the reference numeral designates a section of circular wave guide formed with a flange 11 at one end to facilitate connection to additional wave guide sections or to load devices. The wave guide 10 has an inside diameter large enough to propagate energy produced by the magnetron in the T1544 mode, but small enough to make the operating frequency of the magnetron below the cutofi frequency of all higher modes. A wave guide 12 of H-shaped cross-section is attached to the other end of the circular wave guide 10. This H-shaped wave guide 12 has a restricted central section 13 and wide outer sections 14. The design of suitable guides for this purpose is discussed at page 198 of Microwave Magnetrons by George B. Collins, vol. 6, of the'Radiation Laboratory Series. This wave guide section 12 communicates with a resonant cavity 15 formed in the. anode block of the magnetron 16 through a passage 17. A disk 18 of ceramic material is sealed to the inner walls of the wave guide 10. If the section of wave guide connecting the circular and rectangular Wave guides is mismatched or if the circular and rectangular wave guides are directly connected, the spacing of the disk 18 from the flange 11 is critical and must be carefully selected; otherwise, it is not critical.

If it is necessary to assure that the device will preferentially couple energy of the undesired wave length from the magnetron to the load, the dielectric disk 18 may be given a thickness equal to an integral number of half guide wave lengths of the desired mode of oscillation. The number of half wave lengths will be such that the disk will be of a thickness of an odd number of quarter wave lengths at the undesired frequency and spaced an integral odd number of quarter guide wave lengths of one of the undesired frequencies from the effective beginning of the transformer section of the wave guide 12. These dimensions are optimum and can be varied to some extent without seriously affecting the functioning of the device.

Instead of the H-shaped transformer section of wave guide 12, shown in Figs. 1 and 2, a section of wave guide of rectangular cross-section, such as that shown in Figs. 3 and 4, can be used for the same purpose. In this embodiment of the invention, as before, a disk 20 of dielectric material is positioned within the central portion of a section of circular wave guide 21. The rectangular crosssection of the impedance transformer section 22 is best seen in Fig. 4. Since the TE11 mode will propagate in the circular wave guide, and the TEo1 mode will propagate in the rectangular wave guide, the wide dimension of the rectangular guide (b) must be approximately the same as the diameter of the circular wave guide. In the region where the rectangular wave guide 22 meets the circular wave guide 21, there is a region of curved taper 23. While this taper is optional, it serves to reduce the discontinuity. The impedance transformer section of wave guide 22 may be connected to a resonant cavity of a magnetron or other source of electromagnetic energy in much the same manner as shown in Figs. 1 and 2. The dimensions of this second embodiment of the invention are selected in a similar manner to those of the embodiment shown in Figs. 1 and 2.

This invention is not limited to the particular details of construction, materials and processes described. as many equivalents will su gest themselves to those skilled in the art. It is, accordingly, desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A microwave oscillator for producing oscillations of a desired frequency and an undesired frequency compris ing an electron tube of the magnetron type having an evacuated resonant cavity, a load of high impedance, a device for transmitting electromagnetic energy of the desired frequency from the cavity to the load comprising a section of circular wave guide, an impedance transform ing section of wave guide coupling said cavity to said circular wave guide, a vacuum-tight transverse partition in said wave guide of a thickness equal to an integral number of half wave lengths at the desired frequency and approximately an integral odd number of quarter wave lengths at the undesired frequency positioned an integral odd number of quarter guide wave lengths at the undesired frequency from the efiective junction of the transformer section and the circular wave guide, and means for coupling said circular wave guide to said load.

2. A device for transmitting electromagnetic energy of a desired frequency from an evacuated source also producing energy at an undesired frequency to an external load of high impedance comprising a section of circular wave guide having a vacuum-tight transverse partition of a thickness equal to an integral odd number of half guide wave the circularwave gm an integral odflnumberficf qnarter'guide' wavelengths at 'tlie-undesiredfre'quency. V

3% "Adev icefor-transmittingjeiectmmagnet'ie energyr of.

Tengthseat meadesimrlriflequency and approximately an integral odd number of quarter guide wave lengths at the uticfiesii-edfrequency, and'an impedance transforming section of wave guide joined to one end of the circular guide, said partition beings jacedfrom theeffectivet junctiontof e: and" the transfbrming. section :by

a? dbsired frequency from: an evacuated source of "energy 213 desired and anundesiredfi'equencyitoan external load of high: impedance comprising a section" of circular wavg-guide'havinga vacuum-tight transverse partition of a tfiickness'equal tc an integral numfier of half guide wave {lengths at thedesired frequency"and" approximately {an 1 integral-add numberofquarterr guide-wave lengths at the 4? undesired frequency spaced from the entrance to the circular waveguide. by, an. integral. o dd.numben at quarter guide wave lengths at the undesired frequency.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2;40t7;9v=1 1 Tonksu" .Sptfi L7; 194 2,409,913 Tonks Oct. 22, 194$ 2;4 121;534'-. Fcx; 'Nov-.- 26,4946 252331 55 Shoupp Sept. .19} 1950 2,530,171: Gkress: 'N0v."1='4; '1950 2,555,349 Litton. June 5, 1951 2,576,186 "Miflter "Nov.-"27, 1951 

